Constant temperature controller

ABSTRACT

A constant temperature controller inexpensive and easy to operate, yet capable of accurately controlling the temperature with significantly reduced heat energy consumption, is provided. An operation mode of a cooler is switched between an idling mode and a loaded mode, based on a difference in temperature between a first temperature sensor and a third temperature sensor. For switching the operation mode, cooling power of the cooler is adjusted by changing a frequency of an inverter driving a compressor. Under the loaded mode, the cooling power of the cooler is adjusted by an aperture of an electronic expansion valve such that a difference between a temperature of a second sensor and a target temperature of a heater becomes a constant value.

FIELD OF THE INVENTION

The present invention relates to a constant temperature controller for maintaining the temperature of an external heat load apparatus constant, and more particularly to a constant temperature controller that circulates a heat medium fluid of a constant temperature so as to maintain the temperature of the external heat load apparatus constant, employed for a chiller incorporated in a semiconductor manufacturing apparatus, or the like.

DESCRIPTION OF THE RELATED ART

A conventional constant temperature controller, generally called a chiller, is designed to circulate a heat medium fluid through a pipeline arranged in a loop through a cooler, a heater and an external heat load apparatus, so as to once supercool the liquid medium heated by the external heater with the cooler, and to heat the supercooled liquid medium with the heater thus to supply the external heat load apparatus with the liquid medium of a predetermined temperature specified by the external heat load apparatus.

In such controller, normally the cooler is constantly outputting the rated cooling power irrespective of whether the external heat load apparatus is working. This leads to continuous consumption of a large power, especially when a refrigerator is employed as the cooler. Therefore, JP-A 2004-169933 proposes a constant temperature controller that can switch between an operation mode and an energy-saving mode according to the operation status of the external heat load apparatus.

Also, the cooler of the constant temperature controller is usually set such that the liquid medium is cooled to the specified temperature at the outlet port of the cooler. However, the temperature of the liquid medium often becomes considerably higher (overshoot) or lower (undershoot) than the specified temperature after once reaching the specified temperature, because of slow heat transmission of a coolant gas (such as a CFC gas) in the refrigerator cycle of the cooler. This requires a larger capacity of the heater, and hence a larger heater capable of controlling a wider temperature range has to be employed.

Accordingly, JP-A 2001-153518 proposes providing a temperature controller, outside the constant temperature controller and close to the external heat load apparatus, for micro-adjusting the temperature of the heat medium.

[Patented document 1] JP-A 2004-169933

[Patented document 2] JP-A 2001-153518

The JP-A 2004-169933 discloses a chiller controller that employs a computer that pre-reads recipe information on a process sequence of a plasma etching processor, so as to switch the chiller to the operation mode or to the energy-saving mode, when the etching process enters a certain duration of downtime or when the etching process is resumed.

Such chiller controller, however, requires the computer and associated wires and so on, for constantly monitoring the operation status of the apparatus under the temperature control, and transmitting the status information to the control system of the chiller.

The JP-A 2001-153518 discloses a temperature control system that includes a second temperature controller separated from the chiller and located close to the processing apparatus to be controlled, for setting the temperature at the outlet port of the chiller and micro-adjusting the temperature of the heat medium supplied to the processing apparatus, depending on the temperature of the processing apparatus. Such system, however, incurs a greater heat energy loss because of including two temperature controllers which naturally requires two power supply systems. The system also requires two signal line systems for operating the two controllers, thus making the operation process more complicated.

Accordingly, it is an object of the present invention to provide a constant temperature controller having an operation mode switching function that enables performing the energy-saving operation.

It is another object of the present invention to provide a constant temperature controller inexpensive and easy to operate, yet capable of accurately controlling the temperature with significantly reduced heat energy consumption.

SUMMARY OF THE INVENTION

The present invention provides a constant temperature controller that circulates a heat medium fluid through a fluid path arranged in a loop through a cooler, a heater and an external heat load apparatus so as to maintain the external heat load apparatus at a predetermined constant temperature, comprising a cooler operation mode switch that selects one of the cooler operation modes at least including an idling mode of outputting a minimal cooling power to maintain the temperature when the external heat load is off, and a loaded mode of increasing or decreasing the cooling power according to the external heat load, based on a difference between a heat medium fluid temperature at an inlet port of the cooler and a heat medium fluid temperature at an outlet port of the heater; and a cooling power controller that adjusts the cooling power of the cooler such that the difference between the heat medium fluid temperature at an outlet port of the cooler and a target temperature of the heater becomes a predetermined target difference in temperature under the loaded mode.

The cooler operation mode is switched based on the difference between the circulating heat medium fluid temperature at the inlet port of the cooler and the circulating heat medium fluid temperature at the outlet port of the heater. A reason of such arrangement may be described as follows. It is impossible to precisely foresee when the heat load that has been changed returns from the external heat load apparatus, i.e. the object of the temperature control. The target temperature of the heater, which is the target temperature of the constant temperature controller, is often changed depending on the operation status of the external heat load apparatus. Although the target temperature of the constant temperature controller is changed, the heat load that has been changed may not always return from the external heat load apparatus after the temperature of the heat medium fluid at the outlet port of the constant temperature controller has reached the newly set target and has been stabilized. The heat load that has changed may return during the transition of the temperature toward the target newly set by the constant temperature controller.

Under the conventional control system of switching the operation mode based on the difference between the circulating fluid temperature at the inlet port of the cooler and the target temperature of the constant temperature controller, the heat load that has been changed may return during the transition of the target temperature of the constant temperature controller, i.e. before the circulating fluid temperature at the outlet port of the constant temperature controller reaches the newly set target, in which case the actual temperature becomes considerably higher (overshoot) or lower (undershoot) than the target temperature.

To avoid this, the present invention switches the operation mode based on the difference between the circulating fluid temperature at the inlet port of the cooler and the circulating fluid temperature at the outlet port of the heater. Such method enables quickly detecting the fluctuation in the difference in temperature even during the transition of the target temperature of the constant temperature controller, to thereby quickly react the fluctuation of the lead load, thus allowing switching the operation mode under a stabilized situation without overshooting or undershooting the target temperature by far. As a result, the operation mode can be timely switched and therefore the operation status can be quickly stabilized.

The difference in the circulating fluid temperature varies depending on the type or scale of the external heat load apparatus, as well as of the constant temperature controller, but may be usually set in a range of 1 to 5 degree centigrade. For measuring the temperature difference, a first temperature sensor is disposed at the inlet port of the cooler, and a third temperature sensor at the outlet port of the heater.

The operation mode of the cooler may be switched by switching a frequency of an inverter driving a compressor incorporated in the refrigerator cycle of the cooler. Specifically, the compressor is driven by a low inverter frequency in the idling mode. Driving under a low frequency can reduce the cooling power.

Also, driving the inverter with a low-frequency power reduces the power consumption. In the idling mode real-time adjustment of the cooling power is not required because the heat load scarcely returns from the external heat load apparatus, and it is sufficient to output a low cooling power generally constantly. Such operation mode can be performed over the entire rated temperature range of the constant temperature controller.

In the loaded mode, the compressor of the refrigerator cycle is driven by a power of a high inverter frequency. Increasing the inverter frequency can increase the cooling power. However, since controlling the compressor by the inverter frequency does not provide a sufficiently quick response, the inverter frequency is fixed in the loaded mode, and an electronic expansion valve is employed for controlling the cooling power of the cooler.

Another reason of fixing the inverter frequency of the refrigerator in the loaded mode is that the coolant gas (such as a CFC gas becomes temporarily unstable because of a fluctuation in the inverter frequency, thus degrading the temperature adjusting accuracy.

Also, the fluctuating heat load returns from the external heat load apparatus in the loaded mode, and hence the cooling power of the cooler has to be adjusted at real time in response to the heat load fluctuation. Accordingly, it is preferable to employ the electronic expansion valve which can quickly react, for adjusting the cooling power of the cooler in the loaded mode by controlling the aperture of the valve.

The aperture of the electronic expansion valve is to be adjusted such that the difference between the circulating fluid temperature at the outlet port of the cooler and the target temperature of the heater becomes a predetermined value (hereinafter, “target difference in temperature”). It is preferable to set the target difference in temperature so as to secure a heating margin of the heater, specifically such that the circulating fluid temperature at the outlet port of the cooler becomes several degree centigrade lower, for example 1 to 5 degree centigrade lower than the target temperature of the heater. For such purpose, a second temperature sensor is provided for measuring the circulating fluid temperature at the outlet port of the cooler.

The aperture of the electronic expansion valve may be controlled based on feedback of the circulating fluid temperature at the outlet port of the cooler.

For performing the feedback control, the circulating fluid temperature at the outlet port of the cooler is divided in advance into a plurality of temperature zones, so as to adjust the cooling power of the cooler according to the respective temperature zones.

Hereinafter, the temperature zone of a certain range around a temperature lower than the target temperature of the heater by a predetermined value will be referred to as a target temperature zone, and a zone higher than the target temperature zone as a higher temperature zone, while a zone lower than the target temperature as a lower temperature zone.

When the circulating fluid temperature at the outlet port of the cooler is within the target temperature zone, the aperture of the electronic expansion valve is maintained as it is. When the circulating fluid moves up to the higher temperature zone, which is higher than the target temperature zone, the aperture of the electronic expansion valve is gradually increased so as to increase the cooling power. On the other hand, when the circulating fluid moves down to the lower temperature zone, which is lower than the target temperature zone, the aperture of the electronic expansion valve is gradually reduced so as to decrease the cooling power. Setting thus a certain range in the temperature based on which the valve aperture is controlled allows improving the stability of the circulating fluid temperature.

More specifically, when the circulating fluid of +30 degree centigrade is to be supplied to the external heat load apparatus, the cooler is set so as to maintain the target difference in temperature that is 1 to 5 degree centigrade lower than +30 degree centigrade, at the outlet port. When the target difference in temperature is set as 2 degree centigrade for example, the target temperature becomes +28 degree centigrade. In this case, the expansion valve opens or closes even when the circulating fluid temperature is only 0.1 degree centigrade higher or lower than +28 degree centigrade, which leads to lack of stability in the circulating fluid temperature. Accordingly, granting a certain range to the target temperature, such as +28.5 to +27.5 degree centigrade, the aperture of the expansion valve is not changed within this range, and the circulating fluid temperature can be stabilized.

The target temperature of the heater means the target temperature of the constant temperature controller, which may be changed depending on the type or operation status of the external heat load apparatus.

The heater also has the feedback control function so as to adjust the circulating fluid temperature at the target temperature at the outlet port thereof.

To perform the feedback control, a PID control function may be introduced. Employing the PID control function enables controlling the circulating fluid temperature at the outlet port of the constant temperature controller extremely accurately.

The operation modes of the cooler may further include a temperature increasing mode and a temperature decreasing mode. The temperature increasing mode is performed when the target temperature of the constant temperature controller is changed to a higher temperature, so as to increase the temperature up to the newly set higher target temperature. In this mode, the cooling power is reduced to a minimal level, and a maximal heating power is output thus to increase the temperature as quickly as possible.

The temperature decreasing mode is performed when the target temperature of the constant temperature controller is changed to a lower temperature, so as to decrease the temperature down to the newly set lower target temperature. In this mode, the cooling power is increased and the heating power is turned off thus to decrease the temperature as quickly as possible. The switching between the temperature increasing mode and the temperature decreasing mode is automatically or semi-automatically performed when the target temperature of the constant temperature controller is changed.

The constant temperature controller according to the present invention includes the cooler operation mode switch that selects the cooler operation mode based on the difference between the circulating fluid temperature at the inlet port of the cooler and the circulating fluid temperature at the outlet port of the heater. Such configuration allows quickly detecting the fluctuation in the difference in temperature of the constant temperature controller even during the transition of the target temperature, to thereby quickly react the fluctuation of the lead load, thus allowing switching the operation mode under a stabilized situation without overshooting or undershooting the target temperature by far. As a result, the operation mode can be timely switched and therefore the operation status can be quickly stabilized.

The constant temperature controller according to the present invention includes the cooling power controller that adjusts the cooling power by the inverter frequency that drives the compressor in the refrigerator cycle, and is therefore capable of switching the cooler operation mode between the idling mode and the loaded mode, and thereby performing the energy-saving operation.

The constant temperature controller according to the present invention includes the cooling power controller that adjusts the cooling power by controlling the aperture of the electronic expansion valve provided in the refrigerator cycle, which enables quickly changing the temperature under the loaded mode, as well as performing extremely accurate temperature control of the cooler.

The constant temperature controller according to the present invention includes the cooling power controller that adjusts the cooling power of the cooler such that the difference between the circulating fluid temperature at the outlet port of the cooler and the target temperature of the heater becomes a predetermined target difference in temperature. Such configuration enables maintaining the temperature of the circulating fluid flowing into the heater at a generally constant level, and setting the target difference in temperature in a small range can reduce the influence of the fluctuation of the heat load returning from the external heat load apparatus, which permits selecting a heater of a quite small output, such as an electric heater, yet controlling the circulating fluid temperature flowing out of the heater, quite accurately and at real time.

The constant temperature controller according to the present invention includes the temperature control function of dividing the temperature range of the circulating fluid at the outlet port of the cooler into a plurality of predetermined temperature zones, and utilizing the electronic expansion valve that controls the cooling power of the cooler according to the respective temperature zones. Such method grants a reasonable margin to the temperature based on which the aperture of the electronic expansion valve is to be controlled, thereby improving the stability of the temperature.

The constant temperature controller according to the present invention employs the heater with the PID feedback control function, which allows employing a small-sized electric heater thus to perform the energy-saving operation, as well as accurately controlling the temperature of the circulating fluid supplied to the external heat load apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically showing a configuration of a constant temperature controller according to the present invention;

FIG. 2 is a circuit diagram of the constant temperature controller according to the present invention;

FIG. 3 is a circuit diagram of a control system of the constant temperature controller according to the present invention;

FIG. 4 is a flowchart showing a controlling method of the constant temperature controller according to the present invention;

FIG. 5 is a block diagram for explaining an operation of the constant temperature controller according to the present invention under an idling mode;

FIG. 6 is a block diagram for explaining an operation of the constant temperature controller according to the present invention under a loaded mode (under a large heat load); and

FIG. 6 is a block diagram for explaining an operation of the constant temperature controller according to the present invention under a loaded mode (under a small heat load).

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of the present invention will be described hereunder, referring to the accompanying drawings.

First Embodiment

FIG. 1 is a block diagram schematically showing a configuration of a constant temperature controller, in which a portion enclosed by broken lines constitutes the constant temperature controller 1. The constant temperature controller 1 includes a cooler 2 and a heater 4. Numeral 5 designates an external heat load apparatus to be maintained at a constant temperature, such as an etching apparatus for semiconductor wafers, connected to the constant temperature controller via a pipeline 6 for a circulating fluid so as to constitute a closed loop.

In the pipeline 6, water is sealed in to serve as a heat medium. To the pipeline 6, temperature sensors for measuring the temperature of the heat medium are attached at some points. 41 designates a first temperature sensor that measures the circulating fluid temperature at the inlet port of the cooler, i.e. the temperature of the circulating fluid returning from the external heat load; 42 a second temperature sensor that measures the circulating fluid temperature at the outlet port of the cooler; and 43 a third temperature sensor that measures the circulating fluid temperature at the outlet port of the heater.

FIG. 2 is a circuit diagram showing a configuration of the constant temperature controller, in which a portion enclosed by broken lines corresponds to the constant temperature controller 1 including the cooler 2 and the heater 4 enclosed by dash-dot lines. The constant temperature controller is connected to the external heat load via the pipeline 6. Accordingly, a circulating fluid inlet port 64 and a circulating fluid outlet port 65 are provided.

The cooler 2 includes a compressor 21, a condenser 22, and a heat exchanger 26 connected via a coolant circuit 7 so as to constitute a refrigerator cycle. The coolant circuit 7 includes a first electronic expansion valve 23, a second electronic expansion valve 24, a third electronic expansion valve 25, a separator 27 and so forth. The condenser 22 serves to cool the coolant in the coolant circuit 7 with cooling water in a cooling water circuit 8, to thereby liquidize the coolant.

In FIG. 2, numeral 70 designates a drier (D: a filter including a drying agent to remove moisture from the coolant gas), 71 a strainer (a mesh-type filter for the coolant gas), 72 a sight glass (SG: a window for confirming therethrough the liquidizing status of the coolant gas), 73 a pressure sensor (for detecting higher-pressure side coolant gas pressure), 74 a lower-pressure side service valve (an access point utilized for sealing the coolant gas or maintenance work), 75 a pressure sensor (for detecting lower-pressure side coolant gas pressure) 76 a higher-pressure side service valve (an access point utilized for sealing the coolant gas or maintenance work), 77 a temperature sensor (a fourth sensor that measures the temperature of the coolant gas discharged from the refrigerator), 78 a hot gas bypass circuit (for utilizing compression heat of the coolant gas), 79 an injection circuit (for lowering the temperature of the coolant gas aspirated by the refrigerator to thereby protect the refrigerator), 81 an inlet port of the cooling water, and 82 an outlet port of the cooling water.

The coolant compressed by the compressor 21 is forwarded to the condenser 22 to be cooled by the cooling water flowing through the cooling water circuit 8, thus to be liquidized. The liquidized coolant is adiabatically expanded by the first electronic expansion valve 23 and quickly loses the temperature. The coolant with the dropped temperature exchanges heat with the circulating fluid at the heat exchanger 26, to thereby cool the circulating fluid to the desired temperature. The coolant which has thus gained temperature is vaporized by a separator 30, and introduced into the compressor again.

The electronic expansion valve 23 mainly serves to control the cooling power of the cooler 2. The second electronic expansion valve 24 serves to protect the compressor 21, and the third electronic expansion valve 25 to auxiliarily adjust the cooling power of the cooler 2. The circuit including the electronic expansion valve 25 is referred to as the hot gas bypass circuit, which introduces the coolant gas compressed by the refrigerator and hence having compression heat directly into the heat exchanger 26 instead of cooling the gas in the condenser 22, for exchanging the heat thus to collect heating energy, for adjusting the cooling power when the cooling power has temporarily become excessively large.

The aperture of the electronic expansion valves is adjusted by stepping motors 27, 28, 29.

The heater 4 serves to heat the circulating fluid, which has been supercooled at the heat exchanger 26 in the cooler 2 upon returning from the external heat load apparatus though a return pipeline 61, up to a target temperature. The circulating fluid heated up to the target temperature is forwarded by the pressure of a pump 66, to be supplied to the external heat load apparatus via a feed pipeline 63.

FIG. 3 is a circuit diagram of a controller 11 that controls the cooler 2 and the heater 4. The controller 11 switches a frequency control signal of an inverter 13 that drives the compressor 21 of the cooler 2, based on a difference in temperature between the circulating fluid returning from the external heat load apparatus measured by the first temperature sensor 41 and the circulating fluid forwarded from the heater 4 measured by the third temperature sensor 43, to thereby switch the operation mode of the cooler 2. Here, numeral 12 designates a display/input panel.

When the temperatures measured by the first temperature sensor 41 and the third temperature sensor 43 are barely different, i.e. when the external heat load apparatus is off, the controller selects an idling mode, in which the frequency of the inverter 13 is lowered thus to drive the compressor 21 of the refrigerator cycle at a lower inverter frequency. Driving the inverter at a lower frequency reduces the power consumption of the inverter. Concurrently the controller reduces the aperture of the first electronic expansion valve 23, to thereby reduce the cold energy supplied to the heat exchanger to a minimal level that can maintain the target temperature of the constant temperature controller.

When the difference in temperature between the first temperature sensor 41 and the third temperature sensor 43 exceeds a predetermined threshold value, i.e. when the external heat load apparatus resumes the operation, the controller 11 selects a loaded mode, in which the compressor 21 of the refrigerator cycle is driven at a higher inverter frequency so as to increase the cooling power. Concurrently the controller 11 transmits a control signal to the stepping motor 27 so as to increase the aperture of the first electronic expansion valve 23 thus to increase the cooling power of the cooler 2, and supplies the necessary cold energy to the heat exchanger 26.

In the loaded mode, however, the external heat load is not constant, and hence the cooling power has to be controlled according to the external heat load. For performing such control, the aperture of the electronic expansion valve is adjusted such that a difference between the temperature detected by the second temperature sensor 42 and the target temperature of the heater 4 constantly remains the same. Here, it suffices that the difference in temperature can secure a heating margin for an electric heater 44 of the heater 4.

Maintaining the difference between the circulating fluid temperature at the outlet port of the cooler 2 and the target temperature of the heater 4 at a constant level leads to maintaining the load applied to the heater 4 at a constant level. Applying a constant load makes it easier to control the temperature with the heater 4, resultantly enabling accurately controlling the circulating fluid temperature flowing out of the heater 4. Also, setting the temperature difference in a narrower range can reduce the heating output of the heater 4.

The electric heater 44 is subjected to a PID control, so that the target temperature of the heater 4 and the circulating fluid temperature detected by the third temperature sensor 43 becomes the same.

The target temperature of the heater may be changed depending on a type or operation status of the external heat load apparatus.

The circulating pump 66 is located on an upstream side of the third temperature sensor 43. This is because the work heat of the pump 66 can serve as the heating source in addition to the heater 4, which leads to reduction of the power consumption, and also to more accurate measurement of the temperature of the circulating fluid supplied to the external heat load apparatus.

Referring now to FIG. 4, descriptions will be given hereunder on the operation mode switching function of the constant temperature controller according to the present invention, and the control method of the cooling power of the cooler 2 under each operation mode.

To start with, the target temperature SV of the constant temperature controller is input, and the temperature TS1 of the first temperature sensor 41, the temperature TS2 of the second temperature sensor 42, and the temperature TS3 of the third temperature sensor 43 are read in at the step 91.

At the step 92, the value of TS3-TS1 is compared with the target difference in temperature, and when the former is smaller the process advances to the step 93 of the idling mode. If the former is greater, the process advances to the step 95 of the loaded mode. At the step 93, the frequency of the inverter driving the compressor 21 is lowered to decrease the cooling power of the cooler 2. At the step 94, the aperture of the electronic expansion valve 27 is adjusted for the idling mode. At the step 95 under the loaded mode, the inverter frequency is increased. At the step 96, the value obtained from (target temperature SV-temperature TS2 of the second temperature sensor) and the target difference in temperature are compared, and if the former is smaller the process advances to the step 97, where the aperture of the electronic expansion valve ELV1 is reduced.

If the former is greater, the process advances to the step 98, where the aperture of the electronic expansion valve ELV1 is increased. At the step 99, the heater 4 is subjected to the PID control both under the idling mode and the loaded mode, such that the circulating fluid temperature at the outlet port of the heater reaches the target temperature.

The following passages describe specific examples of the operation of constant temperature controller according to the present invention.

The target difference in temperature A represents the difference between the temperature measured by the first temperature sensor 41 and the temperature measured by the third temperature sensor 43, which will be set as 3 degree centigrade.

The target difference in temperature B represents the difference between the temperature measured by the second temperature sensor 42 and the target temperature of the heater 4, which will be set as −2 degree centigrade.

FIG. 5 is a block diagram showing an operation under the idling mode with the external heat load turned off.

In the example of FIG. 5, the external heat load is 0 W, the temperature measure by the first temperature sensor 41 is 30 degree centigrade, the temperature measured by the second temperature sensor 42 is 29 degree centigrade, the temperature measured by the third temperature sensor 43 is 30 degree centigrade, the energy consumption by the cooler is −500 W, and the energy consumption by the heater is +500 W.

FIG. 6 is a block diagram showing an operation under the loaded mode with a large heat load.

In the example of FIG. 6, the external heat load is +3000 W, the temperature measure by the first temperature sensor 41 is 36 degree centigrade, the temperature measured by the second temperature sensor 42 is 28 degree centigrade, the temperature measured by the third temperature sensor 43 is 30 degree centigrade, the energy consumption by the cooler is −4000 W, and the energy consumption by the heater is +1000 W.

FIG. 7 is a block diagram showing an operation under the loaded mode with a small heat load.

In the example of FIG. 7, the external heat load is +1500 W, the temperature measure by the first temperature sensor 41 is 33 degree centigrade, the temperature measured by the second temperature sensor 42 is 28 degree centigrade, the temperature measured by the third temperature sensor 43 is 30 degree centigrade, the energy consumption by the cooler is −2500 W, and the energy consumption by the heater is +1000 W.

When the target difference in temperature is thus defined on the assumption that 1 degree centigrade corresponds to an amount of heat of 500 W and the operation is accordingly controlled, the target difference in temperature A of 3 degree centigrade means that the heat load of 1500 W has returned. Likewise, the target difference in temperature B of −2 degree centigrade means that the heat load that has returned is supercooled by the cooler by an amount of −1000 W, and that the heater is subjected to the PID control so as to accurately control the temperature with respect to the amount of +1000 W.

When the target difference in temperature B is set as −1 degree centigrade, the cooler supercools the circulating fluid by −500 W, which leads to reduced energy consumption by the heater for executing the control.

The following passages cover a difference in thermal efficiency between a conventional constant temperature controller (including a large heater because of not including the cooler operation switching function and the cooling power controlling function) and the constant temperature controller according to the present invention, when operated under the same condition.

In the conventional constant temperature controller, the cooler is constantly outputting a certain cooling power irrespective of an amount of the heat load returning from the object of the temperature control (external heat load apparatus). Accordingly, when the heat load returning from the object of the temperature control is small, an excessive cooling power is consumed and hence the heater has to output as much energy, in order to control the circulating fluid temperature.

Further, when the external heat load is off and no heat load is returning, the heater has to output a power substantially equivalent to the cooling power of the cooler, for controlling the circulating fluid temperature. This naturally requires a large-scaled heater, thus resulting in greater energy consumption.

Table 1 shows a comparison between the conventional constant temperature controller and the constant temperature controller according to the present invention, on the assumption that the maximum cooling power of the constant temperature controller is 5000 W, and that the energy required for heating or cooling by 1000 W is indicated as 1. TABLE 1 Without With heat load heat load A B A B Heat load from 0 0 3000 3000 external apparatus Cooling power(1) 5000 1000 5000 4000 Heating power(2) 5000 1000 2000 1000 Energy 5 + 5 = 10 1 + 1 = 2 5 + 2 = 7 4 + 1 = 5 consumption(1) + (2) Remarks Idling Loaded mode mode A = Conventional constant temperature controller B = Constant temperature controller of the present invention

As is apparent from Table 1, the total energy consumption of the conventional constant temperature controller with and without the heat load is 10+7=17, while that of the present invention is 2+5=7, which corresponds to energy saving of approx. 60% with respect to the conventional constant temperature controller. 

1. A constant temperature controller that circulates a heat medium fluid through a fluid path arranged in a loop through a cooler, a heater and an external heat load apparatus so as to maintain the external heat load apparatus at a predetermined constant temperature, comprising: a cooler operation mode switch that selects one of the cooler operation modes at least including an idling mode of outputting a minimal cooling power to maintain the temperature when the external heat load is off, and a loaded mode of increasing or decreasing the cooling power according to the external heat load, based on a difference between a heat medium fluid temperature at an inlet port of the cooler and a heat medium fluid temperature at an outlet port of the heater; and a cooling power controller that adjusts the cooling power of the cooler such that the difference between the heat medium fluid temperature at an outlet port of the cooler and a target temperature of the heater becomes a predetermined target difference in temperature, under the loaded mode.
 2. The constant temperature controller according to claim 1, wherein the cooler operation mode switches a frequency of an inverter driving a compressor incorporated in the refrigerator cycle of the cooler, so as to switch the cooler operation mode.
 3. The constant temperature controller according to claim 1, wherein the target difference in temperature of the cooling power controller is set such that the heat medium fluid temperature at the outlet port of the cooler becomes lower than the target temperature of the heater by a predetermined value.
 4. The constant temperature controller according to claim 1, wherein the cooling power controller includes an electronic expansion valve incorporated in the refrigerator cycle of the cooler, so as to adjust the cooling power by controlling the aperture of the electronic expansion valve.
 5. The constant temperature controller according to claim 4, wherein the cooling power controller including the electronic expansion valve includes a feedback control function based on the temperature of the heat medium fluid at the outlet port of the cooler.
 6. The constant temperature controller according to claim 5, wherein the feedback control function includes dividing the heat medium fluid temperature at the outlet port of the cooler into a plurality of temperature zones in advance, and adjusting the cooling power of the cooler according to the respective temperature zones.
 7. The constant temperature controller according to claim 1, wherein the heater includes a feedback control function based on the temperature of the heat medium fluid at the outlet port of the heater.
 8. The constant temperature controller according to claim 7, wherein the feedback control function includes a PID control function. 